The major objective of this proposal is to define requirement of zinc in man. A mild deficiency of zinc is being produced in human volunteers by means of a semipurified diet which supplies all known essential dietary constituents except zinc. Zinc is being assayed in plasma, red cells, white cells and hair at suitable intervals during baseline zinc, depletion and repletion phases. In addition, uptake of 65Zn by red cells in vitro is being measured throughout the study period. Metabolic balance studies are being performed every 4 weeks. These studies are likely to provide criteria for establishing zinc deficient state in man. Correction of zinc deficiency by suitable dietary supplement is likely to yield data which may be used for establishing dietary zinc requirement for man.